Neonatal respiratory disease represents a major source of mortality and morbidity with current management. Mechanical ventilators are used routinely for the support of babies with such disease. Mortality and treatment induced complications occur with considerable frequency. Information which may be applied to improve management is too incomplete to be used predictably regardless of the type of ventilator or severity of illness. It is proposed that infants requiring mechanical ventilation be supported with a system capable of measuring ventilatory parameters, pulmonary-functions and transcutaneous blood gases continuously. The measurements obtained by means of this system will be analyzed by using a computer to determine predictable relationships between the equipment and the patient's pulmonary status. The system uses in addition to the transcutaneous blood gas sensors a ventilator designed to measure a wide range of parameters using a face mask or endotracheal tube without imposing significant additional stress upon the patient. The possible benefits of patient-triggered ventilatory assistance will be included in the assessment. The effectiveness of management will be evaluated by mortality and incidence of complications. The proposed period of extension will permit us to complete the development of this project from the instrumentation and definition of the physiology to the correlation with cardio-pulmonary monitoring by standard, commercial means and to define the implication of changes observed at the bedside.